Alkaline cleaning treatments are employed in a variety of metal forming and coating processes. In the production of steel, cleaning operations to remove oil and debris take place prior to annealing, galvanizing, plating or coating. In aluminum processing, cleaning operations to remove oil and debris precede conversion coating or other coating operations. Satisfactory treatment of such metals requires that any dirt and lubricants from the forming, drawing and ironing operations be removed. Alkaline and acid cleaners are employed in the metal cleaning area. In the cleaning of aluminum, both alkaline and acid cleaners have been employed. Acid etching and cleaning with, for example, hydrofluoric acid gives good results producing clean mirror bright surfaces. However, the use of acids for cleaning present safety and effluent disposal problems and also requires stainless steel equipment. For these reasons, alkaline cleaning and etching processes are favored in the aluminum processing industry. An alkaline cleaning and etching process for aluminum is disclosed in U.S. Pat. No. 4,477,290 to Carroll et. al. The low temperature alkaline cleaning and etching solution for aluminum disclosed comprises alkaline metal hydroxides and a chelating agent at temperatures of from 80 to 130.degree. F. No other ingredients such as wetting agents which would cause foaming problems are required.
U.S. Pat. No. 4,521,332 to Milora discloses a highly alkaline aqueous cleaning dispersion for strip steel which comprises sodium hydroxide, a bulking agent such as sodium carbonate and a poly(acrylic acid) dispersing agent.
With prior art cleaning solutions, the accumulation of oils in the bath presents a three fold problem. First, the presence of oils makes metal cleaning more difficult as the capacity of the surfactants to emulsify oil from the metal becomes limited. Second, in alkaline baths, the oils may saponify and thereby contribute to foaming. Third, subsequent treatment of the affluent must separate out the emulsified oils prior to discharge. Higher treatment levels of surfactants are often used to remedy the problems of insufficient cleaning in the presence of oils. However, this may result in an increase in foam generation and difficulties in breaking the oil/water emulsion prior to discharge of the effluent.